Battery charging device for an electric vehicle

ABSTRACT

An electric vehicle battery charging device includes: a series resonance part, which receives a rectified voltage, and which includes a transformer, a resonant inductor, and a resonant capacitor; a rectifying part, of which a first input end is connected with one end of a secondary winding of the transformer, a second input end is connected with the other end of the secondary winding of the transformer, and an output end is connected with an electric vehicle battery; and a switching part, of which one end is connected with one end of the secondary winding of the transformer and the first input end of the rectifying part, and the other end is connected with the other end of the secondary winding of the transformer and the second input end of the rectifying part, where the switching part controls the current from the secondary winding of the transformer to the rectifying part.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Phase application of PCT International Application No. PCT/KR2012/008960, which was filed on Oct. 29, 2012, and which claims priority from Korean Patent Application No. 10-2011-0140727 filed with the Korean Intellectual Property Office on Dec. 23, 2011. The disclosures of the above patent applications are incorporated herein by reference in their entirety.

BACKGROUND

1. Technical Field

Embodiments of the present invention relate to a battery charging device for an electric vehicle, more particularly to a charging device that ensures a long lifespan and is suitable for charging an electric vehicle battery having a high power density.

2. Description of the Related Art

A device for charging the battery of an electric vehicle (EV) generally uses commercial power. Thus, the battery charging device for an electric vehicle can be used for 110 V_(ac) or 220 V_(ac) and may require consideration of power factor correction. In order to allow charging for batteries of various specifications, the battery charging device for an electric vehicle may be required to provide a wide range of output, such as from 100 V to 500 V.

For this purpose, an electric vehicle battery charging device 100 is generally used that has a dual composition as illustrated in FIG. 1, including an AC/DC converter 110 for power factor correction (PFC), and a high-voltage link capacitor 120 for converting the varying power of AC voltage to a more stable DC power and a DC/DC converter 130 that uses a transformer for charge control.

FIG. 2 is a diagram illustrating the form of power within the conventional battery charging device 100 for an electric vehicle shown in FIG. 1.

Referring to FIG. 2, a conventional charging device 100 for an electric vehicle may rectify an AC input and may perform current control at the power factor correction terminal such that the current at the input side follows the rectified voltage. In this case, fluctuating power occurs, and a high-voltage DC link capacitor may be used for filtering. Then, the DC/DC converter, which uses a transformer for insulation, may charge the battery via current control by using the DC voltage formed at the AC/DC terminal.

However, the conventional electric vehicle charging device 100 described above has a complicated structure, due to its dual composition. Also, the conventional electric vehicle charging device 100 may require an electrolytic capacitor having a high capacitance of several thousand uF or higher and a high power density for filtering the fluctuating power, but since the lifespan of an electrolytic capacitor decreases rapidly at high temperatures, it is not suitable for applications requiring long lifespans, such as electric vehicles.

SUMMARY

To resolve the problem in the related art described above, an aspect of the invention aims to provide a battery charging device for an electric vehicle that ensures a long lifespan and is suitable for charging an electric vehicle battery having a high power density.

One embodiment of the invention provides a battery charging device for an electric vehicle that includes: a series resonance part, which is configured to receive a rectified voltage as input, and which includes a transformer, a resonant inductor, and a resonant capacitor; a rectifying part, of which a first input end is connected with one end of a secondary winding of the transformer, a second input end is connected with the other end of the secondary winding of the transformer, and an output end is connected with an electric vehicle battery; and a switching part, of which one end is connected with one end of the secondary winding of the transformer and with the first input end of the rectifying part, and the other end is connected with the other end of the secondary winding of the transformer and with the second input end of the rectifying part, where the switching part is configured to switch to an on state or an off state for controlling a flow of an electric current from the secondary winding of the transformer to the rectifying part.

Also, another embodiment of the invention provides a battery charging device for an electric vehicle that includes: a series resonance part, which is configured to receive a rectified voltage as input, and which includes a first transformer, a second transformer, a first resonant inductor, a second resonant inductor, and a resonant capacitor; a rectifying part, of which a first input end is connected with one end of a secondary winding of the first transformer and with one end of a secondary winding of the second transformer, a second input end is connected with the other end of the secondary winding of the first transformer and with the other end of the secondary winding of the second transformer, and an output end is connected with an electric vehicle battery; and a switching part, of which one end is connected with one end of the secondary winding of the first transformer, one end of the secondary winding of the second transformer, and the first input end of the rectifying part, and of which the other end is connected with the other end of the secondary winding of the first transformer, the other end of the secondary winding of the second transformer, and the second input end of the rectifying part, where the switching part is configured to switch to an on state or an off state for controlling a flow of an electric current from the secondary winding of the first transformer and the secondary winding of the first transformer to the rectifying part.

According to an embodiment of the invention, the structure of the electric vehicle battery charging device can be simplified, and the dead-zones of an input current can be removed to improve the power factor.

Also, according to an embodiment of the invention, it is possible to extend the lifespan of the electric vehicle battery charging device, to effectively charge an electric vehicle battery having a high power density.

Additional aspects and advantages of the present invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the overall composition of a conventional battery charging device for an electric vehicle.

FIG. 2 illustrates the flow of electrical power in the conventional battery charging device for an electric vehicle illustrated in FIG. 1.

FIG. 3 illustrates the detailed composition of a battery charging device for an electric vehicle according to a first disclosed embodiment of the invention.

FIG. 4 illustrates an operation in a case where there is no switching part present on the secondary circuit of a battery charging device for an electric vehicle according to the first disclosed embodiment of the invention.

FIG. 5 illustrates the operation of a battery charging device for an electric vehicle in a case where the magnitude of the rectified voltage (V_(in)) is greater than or equal to the sum (=2V_(batt)/n) of the voltage applied to the primary winding of the first transformer T₁ and the voltage applied to the primary winding of the second transformer T₂.

FIG. 6A, FIG. 6B, FIG. 7A, and FIG. 7B illustrate the flow of an electric current in a battery charging device for an electric vehicle that is controlled as in FIG. 5.

FIG. 8 illustrates the operation of a battery charging device for an electric vehicle in a case where the magnitude of the inputted rectified voltage (V_(in)) is smaller than the sum (=2V_(batt)/n) of the voltage applied to the primary winding of the first transformer T₁ and the voltage applied to the primary winding of the second transformer T₂.

FIG. 9A, FIG. 9B, FIG. 10A, and FIG. 10B illustrate the flow of an electric current in a battery charging device for an electric vehicle that is controlled as in FIG. 8.

FIG. 11, FIG. 12, FIG. 13, FIG. 14, FIG. 15, FIG. 16, FIG. 17, and FIG. 18 show simulation results for the operation of a battery charging device for an electric vehicle according to the first disclosed embodiment of the invention.

FIG. 19 illustrates the detailed composition of a battery charging device for an electric vehicle according to a second disclosed embodiment of the invention.

DETAILED DESCRIPTION

As the present invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description. However, this is not intended to limit the present invention to particular modes of practice, and it is to be appreciated that all changes, equivalents, and substitutes that do not depart from the spirit and technical scope of the present invention are encompassed in the present invention. In describing the drawings, like reference numerals are used for like components.

When a component is mentioned to be “coupled” or “connected” to another component, this may mean that it is directly coupled or connected to the other component, but it is to be understood that yet another component may exist in-between. On the other hand, when a component is mentioned to be “directly coupled” or “directly connected” to another component, it is to be understood that there are no other components in-between.

Certain embodiments of the invention will be described below in more detail with reference to the accompanying drawings.

FIG. 3 illustrates the detailed composition of a battery charging device for an electric vehicle according to a first disclosed embodiment of the invention.

Referring to FIG. 3, an electric vehicle battery charging device 300 according to the first disclosed embodiment of the invention may include a primary circuit that includes a low-frequency rectifier 310 and a series resonance part 302, a secondary circuit that includes a rectifying part 304 and a switching part 306, and a switching control part 308. The function of each component is described below in more detail.

First, the series resonance part 302 included in the primary circuit may receive an input of a rectified voltage (V_(in)) from the low-frequency rectifier 310 and may include two transformers T₁, T₂, two resonant inductors L_(r1), L_(r2), a resonant capacitor C_(r), four switching elements M₁, M₂, M₃, M₄, and four diodes D₁, D₂, D₃, D₄.

Taking a closer look at the connections between the components within the series resonance part 302, the other end of the first switching element M₁ and one end of the second switching element M₂ may be connected with one end of the primary winding of the first transformer T₁, and a rectified voltage (V_(in)) may be inputted to one end of the first switching element M₁ and the other of the second switching element M₂. Also, the other end of the first diode D₁ and one end of the second diode D₂ may be connected with the other end of the primary winding of the first transformer T₁ (to be more specific, the other end of the first diode D₁ and one end of the second diode D₂ may be connected with the other end of the primary winding of the first transformer T₁ by way of the first resonant inductor L_(r1)), one end of the first diode D₁ may be connected with one end of the first switching element M₁, and the other end of the second diode D₂ may be connected with the other end of the second switching element M₂.

Continuing with the description, the other end of the third switching element M₃ and one end of the fourth switching element M₄ may be connected with the other end of the primary winding of the second transformer T₂ (to be more specific, the other end of the third switching element M₃ and one end of the fourth switching element M₄ may be connected with the other end of the primary winding of the second transformer T₂ by way of the second resonant inductor L_(r2)), and the other end of the third diode D₃ and one end of the fourth diode D₄ may be connected with one end of the primary winding of the second transformer T₂. Also, one end of the third diode D₃ may be connected with one end of the third switching element M₃, one end of the first switching element M₁, and one end of the first diode D₁, and the other end of the fourth diode D₄ may be connected with the other end of the fourth switching element M₄, the other end of the second switching element M₂, and the other end of the second diode D₂.

Further, one end of the resonant capacitor C_(r) may be connected with the other end of the first diode D₁ and one end of the second diode D₂ (i.e. one end of the first resonant inductor L_(r1)), and the other end of the resonant capacitor C_(r) may be connected with the other end of the third diode D₃ and one end of the fourth diode D₄ (i.e. one end of the primary winding of the second transformer T₂). An electrolytic capacitor having a high capacitance or a film capacitor having a small capacitance can be used for the resonant capacitor C_(r). Using a film capacitor having a small capacitance can increase the lifespan and reduce the size of the electric vehicle battery charging device 300.

Next, the rectifying part 304 included in the secondary circuit may be connected with the secondary winding of the transformers T₁, T₂ included in the series resonance part 302 and may operate as a high-frequency rectifier.

To be more specific, a first input end of the rectifying part 304 may be connected with one end of the secondary winding of the first transformer T₁ and with one end of the secondary winding of the second transformer T₂, a second input end of the rectifying part 304 may be connected with the other end of the secondary winding of the first transformer T₁ and with the other end of the secondary winding of the second transformer T₂, and the output end of the rectifying part 304 may be connected with the battery for the electric vehicle (batt). Here, the rectifying part 304 can be composed of four diodes D₅, D₆, D₇, D₈ that are connected in a full bridge configuration.

Furthermore, this switching part 306 included in the secondary circuit may be a component that performs a current-boosting function, and may be switched on or off to control the flow of electric currents from the secondary windings of the transformers T₁, T₂ to the rectifying part 304.

To be more specific, the switching part 306 may have one end connected with one end of the secondary winding of the first transformer T₁, one end of the secondary winding of the second transformer T₂, and the first input end of the rectifying part 304, and may have the other end connected with the other end of the secondary winding of the first transformer T₁, the other end of the secondary winding of the second transformer T₂, and the second input end of the rectifying part 304. When the switching part 306 is switched on, terminal a and terminal b are short-circuited, so that no current is inputted to the rectifying part 304 (i.e. I_(S)=0), and when the switching part 306 is switched off, terminal a and terminal b are made open. Accordingly, the switching part 306 can include a fifth switching element M₅ for controlling the flow of current in one direction and a sixth switching element M₆ for controlling the flow of current in the other direction, as illustrated in FIG. 3.

According to an embodiment, the first switching element M₁ and the fourth switching element M₄ can be turned on/off simultaneously, and the second switching element M₂ and the third switching element M₃ can be turned on/off simultaneously. In this case, the arrangement can be controlled such that the time during which the first switching element M₁ and the fourth switching element M₄ are turned on does not overlap the time during which the second switching element M₂ and the third switching element M₃ are turned on.

In this case, according to an embodiment of the invention, the first switching element M₁, the second switching element M₂, the third switching element M₃, and the fourth switching element M₄ can be switched on/off periodically, and the on/off period of the first switching element M₁, the on/off period of the second switching element M₂, the on/off period of the third switching element M₃, and the on/off period of the fourth switching element M₄ can be equal.

Finally, the switching control part 308 may generate control signals for controlling the switching on/off of the first to fourth switching elements M₁, M₂, M₃, M₄ and the switching part 306 (i.e. the fifth switching element M₅ and sixth switching element M₆). For example, if the first to sixth switching elements M₁, M₂, M₃, M₄, M₅, M₆ are implemented as MOSFET's as illustrated in FIG. 3, the generated control signals may be inputted to the gate electrodes of the six MOSFET's (M₁, M₂, M₃, M₄, M₅, M₆).

A more detailed description of the operation of an electric vehicle battery charging device 300 according to the first disclosed embodiment of the invention is provided below with reference to FIG. 4 through FIG. 10.

FIG. 4 illustrates an operation in a case where there is no switching part 306 present on the secondary circuit of an electric vehicle battery charging device 300 according to the first disclosed embodiment of the invention.

To be more specific, FIG. 4 illustrates changes in the rectified voltage (V_(in)), the resonance current (I_(Lr)) flowing through the resonant inductors L_(r1), L_(r2), and the input current (I_(in)), for a case in which there is no switching part 306 present, the first to fourth switching elements M₁, M₂, M₃, M₄ are switched on/off according to equal periods, the first switching element M₁ and the fourth switching element M₄ are turned on/off simultaneously, the second switching element M₂ and the third switching element M₃ are turned on/off simultaneously, and the time during which the first switching element M₁/fourth switching element M₄ are turned on does not overlap the time during which the second switching element M₂/third switching element M₃ are turned on.

Referring to FIG. 4, if the first to fourth switching elements M₁, M₂, M₃, M₄ are operated as described above and if the turns ratio of the two transformers T₁, T₂ is 1:n, then a voltage of V_(batt)/n would be applied to the primary winding of each of the two transformers T₁, T₂, so that the primary windings of the two transformers connected in series would have a total voltage of 2V_(batt)/n applied thereto.

However, if the magnitude of the rectified voltage (V_(in)) is smaller than 2V_(batt)/n, the first to fourth diodes D₁, D₂, D₃, D₄ would not conduct a current, and therefore dead zones may occur in which there is no input current (I_(in)) and no resonance current (I_(Lr)), as illustrated in FIG. 4. Dead zones may lower the power factor of the electric vehicle battery charging device, and if the voltage of the electric vehicle battery (batt) is lower than the rectified voltage (V_(in)), the electric vehicle battery would not be charged.

An electric vehicle battery charging device 300 according to the first disclosed embodiment of the invention may resolve this problem by having the switching part 306 perform current boosting. A more detailed description of the switching operation of the switching part 306 for resolving the above-described problem is provided below with reference to FIG. 5 through FIG. 10.

FIG. 5 illustrates the operation of an electric vehicle battery charging device 300 in a case where the magnitude of the rectified voltage (V_(in)) is greater than or equal to the sum (=2V_(batt)/n) of the voltage applied to the primary winding of the first transformer T₁ and the voltage applied to the primary winding of the second transformer T₂, while FIG. 6A, FIG. 6B, FIG. 7A, and FIG. 7B illustrate the flow of an electric current in an electric vehicle battery charging device 300 that is controlled as in FIG. 5.

Referring to FIG. 5, if the magnitude of the rectified voltage (V_(in)) is greater than or equal to the sum of the voltage applied to the primary winding of the first transformer T₁ and the voltage applied to the primary winding of the first transformer T₂, the switching control part 308 may, from a state in which the switching part 306 is off (i.e. the fifth switching element M₅ and sixth switching element M₆ are off), switch on the first switching element M₁ and fourth switching element M₄ simultaneously and switch off the second switching element M₂ and third switching element M₃ simultaneously.

Here, the path of the electric current within the electric vehicle battery charging device 300 may be formed as indicated in FIG. 6A, whereby a resonance current (I_(Lr)) may occur in the resonant inductors L_(r1), L_(r2). The resonance current (I_(Lr)) thus generated may be transferred to the secondary circuit by way of the secondary windings of the transformers T₁, T₂ and transferred as output through the fifth diode D₅ and the eighth diode D₈. During this time, the voltage (V_(Cr)) of the resonant capacitor C_(r) may increase from −V_(in) to +V_(in) while resonating.

Continuing with the description, when the magnitude of the voltage (V_(Cr)) of the resonant capacitor C_(r) becomes equal to the magnitude of the rectified voltage (V_(in)), the first diode D₁ and fourth diode D₄ of the primary circuit may conduct a current, and as a result, the path of the electric current within the electric vehicle battery charging device 300 may be formed as indicated in FIG. 6B. Here, the resonance current (I_(Lr)) may decrease linearly with a slope of −V_(batt)/(nL) as it is transferred to the secondary circuit.

Afterwards, when the magnitude of the resonance current (I_(Lr)) becomes 0, there would be no electric current flowing within the electric vehicle battery charging device 300 and the operation of the overall circuit may be halted.

Next, the switching control part 308 may, from a state in which the switching part 306 is off (i.e. the fifth switching element M₅ and sixth switching element M₆ are off), switch on the second switching element M₂ and third switching element M₃ simultaneously, and at the same time, switch off the first switching element M₁ and fourth switching element M₄.

Here, the path of the electric current within the electric vehicle battery charging device 300 may be formed as indicated in FIG. 7A, whereby a resonance current (I_(Lr)) may occur in the resonant inductors L_(r1), L_(r2). The resonance current (I_(Lr)) thus generated may be transferred to the secondary circuit by way of the secondary windings of the transformers T₁, T₂ and transferred as output through the sixth diode D₆ and the seventh diode D₇. During this time, the voltage (V_(Cr)) of the resonant capacitor C_(r) may decrease from −V_(in) to +V_(in) while resonating.

Continuing with the description, when the magnitude of the voltage (V_(Cr)) of the resonant capacitor C_(r) becomes equal to the magnitude of the rectified voltage (V_(in)), the second diode D₂ and third diode D₃ of the primary circuit may conduct a current, and as a result, the path of the electric current within the electric vehicle battery charging device 300 may be formed as indicated in FIG. 7B. Here, the resonance current (I_(Lr)) may increase linearly with a slope of V_(batt)/(nL) as it is transferred to the secondary circuit.

Afterwards, when the magnitude of the resonance current (I_(Lr)) becomes 0, there would be no electric current flowing within the electric vehicle battery charging device 300 and the operation of the overall circuit may be halted.

Briefly put, in cases where the magnitude of the rectified voltage (V_(in)) is greater than or equal to the sum of the voltage applied to the primary winding of the first transformer T₁ and the primary winding of the second transformer T₂, the switching control part 308 may provide control such that the first switching element M₁ and the fourth switching element M₄ are turned on/off simultaneously, the second switching element M₂ and the third switching element M₃ are turned on/off simultaneously, and the time during which the first switching element M₁/fourth switching element M₄ are turned on does not overlap the time during which the second switching element M₂/third switching element M₃ are turned on, as a result of which the battery for an electric vehicle (batt) may be charged. Here, the first to fourth switching elements M₁, M₂, M₃, M₄ can be switched on or off periodically, and the period of switching on/off for the first to fourth switching elements M₁, M₂, M₃, M₄ can be the same.

Thus, the current (I_(s)) flowing through the secondary circuit may have the same form as the resonance current (I_(Lr)) and its magnitude may be 2I_(Lr)/n.

FIG. 8 illustrates the operation of an electric vehicle battery charging device 300 in a case where the magnitude of the inputted rectified voltage (V_(in)) is smaller than the sum (=2V_(batt)/n) of the voltage applied to the primary winding of the first transformer T₁ and the voltage applied to the primary winding of the second transformer T₂, while FIG. 9A, FIG. 9B, FIG. 10A, and FIG. 10B illustrate the flow of an electric current in an electric vehicle battery charging device 300 that is controlled as in FIG. 8.

Referring to FIG. 8, if the magnitude of the rectified voltage (V_(in)) is smaller than the sum of the voltage applied to the primary winding of the first transformer T₁ and the voltage applied to the primary winding of the first transformer T₂, the switching control part 308 may first switch on the first switching element M₁ and fourth switching element M₄ and switch off the second switching element M₂ and third switching element M₃, and at the same time turn on the switching part 306 (i.e. switch on the fifth switching element M₅ and sixth switching element M₆).

Here, the path of the electric current within the electric vehicle battery charging device 300 may be formed as indicated in FIG. 9A. That is, as the switching part 306 is turned on, the secondary winding of the first transformer T₁ and the secondary winding of the second transformer T₂ may be short-circuited, and as a result, the path of the electric current in the series resonance part 302 may be formed in the same manner as described above with reference to FIG. 6A, so that a resonance current (I_(Lr)) may occur in the resonant inductors L_(r1), L_(r2). The resonance current (I_(Lr)) thus generated may be transferred to the secondary circuit by way of the secondary windings of the first transformer T₁ and second transformer T₂, but since it flows through the fifth switching element M₅ and sixth switching element M₆, it may not be conducted through the fifth to eighth diodes D₅-D₈, with no electrical power transferred to the output side. During this time, the voltage (V_(Cr)) of the resonant capacitor C_(r) may increase from −V_(in) to +V_(in) while resonating.

Continuing with the description, when the magnitude of the voltage (V_(Cr)) of the resonant capacitor C_(r) becomes equal to the magnitude of the rectified voltage (V_(in)), the switching control part 308 may turn off the switching part 306 (i.e. the fifth switching element M₅ and sixth switching element M₆). In other words, the switching part 306 may be switched on together with the first switching element M₁ and fourth switching element M₄, and can be switched off at a point when the magnitude of the voltage (V_(Cr)) applied to the resonant capacitor C_(r) becomes equal to the magnitude of the rectified voltage (V_(in)) while the first switching element M₁ and the fourth switching element M₄ are in an on state.

When the magnitude of the voltage (V_(Cr)) of the resonant capacitor C_(r) reaches the magnitude of the input voltage (V_(in)) and the switching part 306 is turned off, the resonance current (I_(Lr)) may decrease linearly with a slope of −V_(batt)/(nL) while it flows through the first diode D₁ and fourth diode D₄, as illustrated in FIG. 9B, to be transferred through the first transformer T₁, second transformer T₂, fifth diode D₅, and eighth diode D₈ to the output side.

Afterwards, when the magnitude of the resonance current (I_(Lr)) becomes 0, there would be no electric current flowing within the electric vehicle battery charging device 300 and the operation of the overall circuit may be halted.

Next, the switching control part 308 may switch off the first switching element M₁ and the fourth switching element M₄, switch on the second switching element M₂ and the third switching element M₃, and at the same time, turn on the switching part 306 (i.e. switch on the fifth switching element M₅ and sixth switching element M₆).

Here, the path of the electric current within the electric vehicle battery charging device 300 may be formed as indicated in FIG. 10A. That is, as the switching part 306 is turned on, the secondary winding of the first transformer T₁ and the secondary winding of the second transformer T₂ may be short-circuited, and as a result, the path of the electric current in the series resonance part 302 may be formed in the same manner as described above with reference to FIG. 7A, so that a resonance current (I_(Lr)) may occur in the resonant inductors L_(r1), L_(r2). The resonance current (I_(Lr)) thus generated may be transferred to the secondary circuit by way of the secondary windings of the first transformer T₁ and second transformer T₂, but since it flows through the fifth switching element M₅ and sixth switching element M₆, it may not be conducted through the sixth and seventh diodes D₆, D₇, with no electrical power transferred to the output side. During this time, the voltage (V_(Cr)) of the resonant capacitor C_(r) may decrease from +V_(in) to −V_(in) while resonating.

Continuing with the description, when the magnitude of the voltage (V_(Cr)) of the resonant capacitor C_(r) becomes equal to the magnitude of the rectified voltage (V_(in)), the switching control part 308 may turn off the switching part 306 (i.e. the fifth switching element M₅ and sixth switching element M₆). In other words, the switching part 306 can be turned on together with the second switching element M₂ and the third switching element M₃, and can be turned off at a point when the magnitude of the voltage (V_(Cr)) applied to the resonant capacitor C_(r) becomes equal to the magnitude of the rectified voltage (V_(in)) while the second switching element M₂ and the third switching element M₃ are in an on state.

When the magnitude of the voltage (V_(Cr)) of the resonant capacitor C_(r) reaches the magnitude of the input voltage (V_(in)) and the switching part 306 is turned off, the resonance current (I_(Lr)) may increase linearly with a slope of V_(batt)/(nL) while it flows through the second diode D₂ and third diode D₃, as illustrated in FIG. 10B, to be transferred through the first transformer T₁, second transformer T₂, sixth diode D₆, and seventh diode D₇ to the output side.

Afterwards, when the magnitude of the resonance current (I_(Lr)) becomes 0, there would be no electric current flowing within the electric vehicle battery charging device 300 and the operation of the overall circuit may be halted.

In summary, looking at the operating waveform in the segment where the magnitude of the inputted rectified voltage (V_(in)) is smaller than 2V_(batt)/n, the current I_(s) flowing through the secondary circuit may be transferred to the output side from the point when the switching part 306 is turned off until the point when the resonance current (I_(Lr)) becomes 0. As such, the waveform of I_(s) has a triangular form.

Next, the switching control part 308 may, from a state in which the switching part 306 is off (i.e. the fifth switching element M₅ and sixth switching element M₆ are off), switch on the second switching element M₂ and third switching element M₃ simultaneously and switch off the first switching element M₁ and fourth switching element M₄ simultaneously.

The operation of the electric vehicle battery charging device 300 here can be symmetrical to the mode of operation described above, and as such, will not be described in further detail.

Briefly put, in cases where the magnitude of the rectified voltage (V_(in)) is smaller than the sum of the voltage applied to the primary winding of the first transformer T₁ and the primary winding of the second transformer T₂, the switching control part 308 may provide control such that the first switching element M₁ and the fourth switching element M₄ are turned on/off simultaneously, the second switching element M₂ and the third switching element M₃ are turned on/off simultaneously, and the time during which the first switching element M₁/fourth switching element M₄ are turned on does not overlap the time during which the second switching element M₂/third switching element M₃ are turned on, with the switching part 305 also turned on at the point when the first to fourth switching elements M₁, M₂, M₃, M₄ are turned on, and with the switching part 305 turned off at the point when the magnitude of the voltage (V_(Cr)) applied to the resonant capacitor C_(r) becomes equal to the rectified voltage (V_(in)) while the first to fourth switching elements M₁, M₂, M₃, M₄ are in an on state, and as a result of the above, the battery for an electric vehicle (batt) may be charged. Here, the first to fourth switching elements M₁, M₂, M₃, M₄ can be switched on or off periodically, and the period of switching on/off for the first to fourth switching elements M₁, M₂, M₃, M₄ can be the same.

Although the descriptions above refer to controlling the on/off state of the switching part 306 only when the magnitude of the rectified voltage (V_(in)) is smaller than the sum of the sum of the voltage applied to the primary winding of the first transformer T₁ and the voltage applied to the primary winding of the first transformer T₂, another embodiment of the invention can entail controlling the on/off state of the switching part 306 even when the magnitude of the rectified voltage (V_(in)) is greater than or equal to the sum of the sum of the voltage applied to the primary winding of the first transformer T₁ and the voltage applied to the primary winding of the first transformer T₂. In such a case, the switching control part 308 can control the series resonance part 302 and the switching part 306 by using the same control signals regardless of the magnitude of the rectified voltage (V_(in)), thereby enabling a more simplified control.

FIG. 11 through FIG. 18 show simulation results for the operation of an electric vehicle battery charging device 300 according to the first disclosed embodiment of the invention. A description of the simulation results is provided below with reference to FIG. 11 through FIG. 18.

First, FIG. 11 to FIG. 13 present graphs that show simulation results obtained when the switching is controlled as in the upper part of FIG. 5, with the Vrms of the rectified voltage (V_(in))(=input voltage (V_(ac))) set to 220 Vrms.

Referring to FIG. 11 to FIG. 13, it can be observed that the input current (I_(in)=I_(ac)) soundly follows the waveform of the input voltage (V_(ac)) and that a high power factor is obtained. Also, a change in the form of the resonance current (I_(Lr)) can be observed, as the switching part 306 (i.e. fifth switching element M₅ and sixth switching element M₆) is operated differently according to the input voltage (V_(ac)), as illustrated in FIG. 12 and FIG. 13.

Also, FIG. 14 presents graphs that show simulation results for the input current (I_(ac)) according to the input voltage (V_(ac)), where it can be observed that a high power factor is ensured over a broad range of input.

Next, FIG. 15 to FIG. 17 present graphs that show simulation results obtained when the switching is controlled as in the upper part of FIG. 8, with the Vrms of the rectified voltage (V_(in))(=input voltage (V_(ac))) set to 220 Vrms.

Referring to FIG. 15 to FIG. 17, it can be observed that there are no segments in which the waveform of the resonance current (I_(Lr)) in FIG. 15 is changed, as the switching part 306 is always operated regardless of the input voltage (V_(ac)).

Also, FIG. 18 presents graphs that show simulation results for the input current (I_(ac)) according to the input voltage (V_(ac)), where it can be observed that a charging operation can be implemented while a high power factor is ensured over a broad range of input.

FIG. 19 illustrates the detailed composition of a battery charging device for an electric vehicle according to a second disclosed embodiment of the invention.

Referring to FIG. 19, an electric vehicle battery charging device 1900 may be substantially the same as the electric vehicle battery charging device 300 described above with reference to FIG. 3, with the exception that, in the series resonance part 1902, the third switching element, the fourth switching element, the third diode, the fourth diode, the second transformer, and the second resonant inductor are removed, and the other end of the resonant capacitor is connected with a ground.

Table 1 shown below lists the corresponding relationships between components of the electric vehicle battery charging device 300 illustrated in FIG. 3 and components of the electric vehicle battery charging device 1900 illustrated in FIG. 19. The features described with reference to FIG. 3 can be applied in the same manner, based on Table 1, to an electric vehicle battery charging device 1900 according to the second disclosed embodiment of the invention.

TABLE 1 First Disclosed Embodiment Second Disclosed Embodiment (FIG. 3) (FIG. 11) first switching element M₁ and first switching element M₁ fourth switching element M₄ second switching element M₂ and second switching element M₂ third switching element M₃ first diode D₁ and fourth diode D₄ first diode D₁ second diode D₂ and third diode D₃ second diode D₂ first resonant inductor L_(r1) and resonant inductor L_(r) second resonant inductor L_(r2) first transformer T₁ and transformer T second transformer T₂ comparison made between magnitude of comparison made between rectified voltage (V_(in)) and 2V_(batt)/n magnitude of rectified voltage (V_(in)) and V_(batt)/n

Thus, further descriptions on the electrical vehicle battery charging device 1100 according to the second disclosed embodiment of the invention are omitted.

While the present invention has been described above using particular examples, including specific elements, by way of limited embodiments and drawings, it is to be appreciated that these are provided merely to aid the overall understanding of the present invention, the present invention is not to be limited to the embodiments above, and various modifications and alterations can be made from the disclosures above by a person having ordinary skill in the technical field to which the present invention pertains. Therefore, the spirit of the present invention must not be limited to the embodiments described herein, and the scope of the present invention must be regarded as encompassing not only the claims set forth below, but also their equivalents and variations. 

What is claimed is:
 1. A battery charging device for an electric vehicle, the battery charging device comprising: a series resonance part configured to receive a rectified voltage as input, the series resonance part comprising a transformer, a resonant inductor, and a resonant capacitor; a rectifying part having a first input end thereof connected with one end of a secondary winding of the transformer, a second input end thereof connected with the other end of the secondary winding of the transformer, and an output end thereof connected with an electric vehicle battery; and a switching part having one end thereof connected with one end of the secondary winding of the transformer and with the first input end of the rectifying part and having the other end thereof connected with the other end of the secondary winding of the transformer and with the second input end of the rectifying part, the switching part configured to switch to an on state or an off state for controlling a flow of an electric current from the secondary winding of the transformer to the rectifying part.
 2. The battery charging device of claim 1, further comprising: a first switching element connected with one end of a primary winding of the transformer; a second switching element connected with one end of the primary winding of the transformer; a first diode connected with the other end of the primary winding of the transformer; and a second diode having one end thereof connected with the other end of the primary winding of the transformer.
 3. The battery charging device of claim 2, wherein the rectified voltage is inputted through one end of the first switching element and the other end of the second switching element, the one end of the first switching element is connected with one end of the first diode, the other end of the second switching element is connected with the other end of the second diode, the other end of the first diode and the one end of the second diode are connected with the other end of the primary winding of the transformer by way of the resonant inductor, one end of the resonant capacitor is connected with the other end of the first diode and the one end of the second diode, and the other end of the resonant capacitor is connected with the other end of the second diode.
 4. The battery charging device of claim 3, wherein a time during which the first switching element is in an on state does not overlap a time during which the second switching element is in an on state.
 5. The battery charging device of claim 4, wherein the first switching element and the second switching element are switched on or off periodically, and a period of switching on or off for the first switching element and a period of switching on or off for the second switching element are equal.
 6. The battery charging device of claim 4, wherein the switching part is switched on together with the first switching element and the second switching element, and is switched off at a point when a magnitude of a voltage applied to the resonant capacitor becomes equal to a magnitude of the inputted rectified voltage while the first switching element and the second switching element are in an on state.
 7. The battery charging device of claim 6, wherein the switching part is switched on together with the first switching element and the second switching element while a magnitude of the inputted rectified voltage is greater than or equal to a voltage applied to the primary winding of the transformer, and is switched off at a point when a magnitude of a voltage applied to the resonant capacitor becomes equal to a magnitude of the inputted rectified voltage while the first switching element and the second switching element are in an on state.
 8. The battery charging device of claim 1, wherein the resonant capacitor is a film capacitor.
 9. The battery charging device of claim 1, wherein the rectifying part comprises four diodes connected in a full bridge configuration.
 10. A battery charging device for an electric vehicle, the battery charging device comprising: a series resonance part configured to receive a rectified voltage as input, the series resonance part comprising a first transformer, a second transformer, a first resonant inductor, a second resonant inductor, and a resonant capacitor; a rectifying part having a first input end thereof connected with one end of a secondary winding of the first transformer and with one end of a secondary winding of the second transformer, a second input end thereof connected with the other end of the secondary winding of the first transformer and with the other end of the secondary winding of the second transformer, and an output end thereof connected with an electric vehicle battery; and a switching part having one end thereof connected with one end of the secondary winding of the first transformer, one end of the secondary winding of the second transformer, and the first input end of the rectifying part and having the other end thereof connected with the other end of the secondary winding of the first transformer, the other end of the secondary winding of the second transformer, and the second input end of the rectifying part, the switching part configured to switch to an on state or an off state for controlling a flow of an electric current from the secondary winding of the first transformer and the secondary winding of the first transformer to the rectifying part.
 11. The battery charging device of claim 10, wherein the series resonance part further comprises: a first switching element having the other end thereof connected with one end of the primary winding of the first transformer; a second switching element having one end thereof connected with one end of the primary winding of the first transformer; a third switching element having the other end thereof connected with one end of the primary winding of the second transformer; a fourth switching element having one end thereof connected with one end of the primary winding of the second transformer; a first diode having one end thereof connected with one end of the first switching element and having the other end thereof connected with other end of the primary winding of the first transformer; a second diode having one end thereof connected with the other end of the primary winding of the first transformer and having the other end thereof connected with the other end of the second switching element; a third diode having one end thereof connected with one end of the third switching element and having the other end thereof connected with one end of the primary winding of the second transformer; and a fourth diode having one end thereof connected with one end of the primary winding of the second transformer and having the other end thereof connected with the other end of the fourth switching element.
 12. The battery charging device of claim 11, wherein the rectified voltage is inputted through one end of the first switching element and the other end of the second switching element, and the other end of the first diode and one end of the second diode are connected by way of the first resonant inductor with the other end of the primary winding of the first transformer.
 13. The battery charging device of claim 12, wherein the other end of the third diode and one end of the fourth diode are connected by way of the second resonant inductor with the other end of the primary winding of the second transformer, one end of the resonant capacitor is connected with the other end of the first diode and one end of the second diode, and the other end of the resonant capacitor is connected with the other end of the third diode and one end of the fourth diode.
 14. The battery charging device of claim 13, wherein the first switching element and the fourth switching element are switched on or off simultaneously, the second switching element and the third switching element are switched on or off simultaneously, and a time during which the first switching element and the fourth switching element are in an on state does not overlap a time during which the second switching element and the third switching element are in an on state.
 15. The battery charging device of claim 14, wherein the first switching element, the second switching element, the third switching element, and the fourth switching element are switched on or off periodically, and a period of switching on or off for the first switching element, a period of switching on or off for the second switching element, a period of switching on or off for the third switching element, and a period of switching on or off for the fourth switching element are equal.
 16. The battery charging device of claim 14, wherein the switching part is switched on together with the first switching element, the second switching element, the third switching element, and the fourth switching element, and is switched off at a point when a magnitude of a voltage applied to the resonant capacitor becomes equal to a magnitude of the inputted rectified voltage while the first switching element, the second switching element, the third switching element, and the fourth switching element are in an on state.
 17. The battery charging device of claim 16, wherein the switching part is switched on together with the first switching element and the second switching element while a magnitude of the inputted rectified voltage is greater than or equal to a sum of a voltage applied to the primary winding of the first transformer and a voltage applied to the primary winding of the second transformer, and is switched off at a point when a magnitude of a voltage applied to the resonant capacitor becomes equal to a magnitude of the inputted rectified voltage while the first switching element and the second switching element are in an on state.
 18. The battery charging device of claim 10, wherein the resonant capacitor is a film capacitor.
 19. The battery charging device of claim 10, wherein the rectifying part comprises four diodes connected in a full bridge configuration. 